Adding a guide to include devices in certification

Change-Id: Id9d59342bdff5e1dfb18cc7e0d1028dfa9f6352e
diff --git a/index.rst b/index.rst
index 8c51b20d..7a94b76 100644
--- a/index.rst
+++ b/index.rst
@@ -170,6 +170,7 @@
    testing/index.rst
    testing/memory_usage_pprof.rst
    testing/voltha_test_automation.rst
+   testing/certification.rst
 
 .. toctree::
    :maxdepth: 1